Electroacoustic device



ay 5, 1936.. w T. TABER 290399855 ELECTROACOUSTIC DEVICE Filed May 27,1929 Tic-1.1..

INVENTOR u ATTORNEY or vice versa, that is, telephone receivers andpositioning the moving coil.

' provided with a field winding and an outer pot- Patented May 5, 1936UNITED STATES PATENT OFFICE ELECTROAOOUSTIO DEVICE William T. Taber,Bloomfield, N. J., assignor, by mesne assignments, to Radio Corporationof America, New York, N. Y., a corporation of Delaware Application May2'7, 1929, Serial No. 366,341 12 Claims. (01. ne -115.5)

This invention relates to electro-acoustic deshaped member ll connectedat one end to one vices of the moving coil, or dynamic, type for end ofthe core l0, and extended inwardly at its converting electricaloscillations into sound waves other end to form an outer pole piecespaced from the pole piece formed by the other end of the core to leavean annular air gap l2. A dished diaphragm l3, conical as shown, ismounted in front of the magnet. The large end of the diaphragm issecured through a flexible portion [4 to the edge of a support or cageIS, The voice coil 20 is mounted ona tubular carrier 2| which is securedto the small or apex end of the diaphragm and extends into the annulargap I2 with the coil located between the magnet poles. The voice coil isfed through leads 22 with an audio-frequency varying current as usual.

, The carrier tube 2| and the small end of the diaphragm are centeredand positioned by means of a flexible disk 25 which is fixedwithin thecarrier tube and extends transversely thereof closely adjacent to theouter edge of the coil, and is secured by means of a screw 26 andspacing washer 21 to the end of the core H1, or inner pole piece. Thedisk 25, while permitting the necessary axial movement of the diaphragmand coil carrier, holds them against transverse movement and insuresaccurate positioning of the coil in the air gap, and makes it possibleto havethe gap very narrow, with a minimum clearance between the coiland its carrier and the gap walls withoutdanger of contact. Mostdesirably, the centering disk is located within the tube close to theplane of the outer edge of the coil, thereby minimizing the effect ofany slight inaccuracy of the parts; Having the centering disk securedwithin the coil carrying tube has the further advantage, especially whenit is located well within the tube as shown, of strengthening the tubeand resisting any tendency to deformation thereof.

The coil carrying tube 21 may be of any suitable material and formed inany suitable manner. I have found it most desirable, however, to makethe tube of paper board and of the construction shown in Fig; 4; As hereshown, the tube comprises an inner tubular member 30 extending the fulllength of the tube, and two spaced outer tubular members 3i and 32spaced apart to form an external circumferential channel 33 forreceiving the voice coil, the spaced outer tubes or bands 3| and 32being of such width respectively and so spaced that the channel 33 is ofdesired Width and located in the desired position longitudinally of thetube. The band 32 will usually be narrow as shown, and the band 3|wider, since the tube need not extendinward substantially beyond theinner edge of the coil, and may even transmitters. The invention relatesmore particularly to means for mounting and transversely It is desirablethat the annular air gap in the magnetic circuit of a dynamic receiveror trans mitter shall be as narrow as possible, but the narrower the gapthe more necessary it becomes to have the moving, or voice, coil and itscarrier, which are mounted free to move axially in the magnetic gap,accurately positioned and held against transverse movement so as toavoid contact with either the inner or outer pole pieces. The presentinvention aims to provide an improved coil carrier and centering meansfor accurately positioning the coil carrier and the diaphragm withrelation to the magnetic gap and holding them against transversemovement, while permitting the required axial movement.

A coil carrier according to the invention is of tubular form and has aflexible disk fixed transversely within the tube for connection to theend of the central pole piece of the magnet. Making the tubular carrierwith such a centering disk secured therein not only simplifiesproduction, but has the important advantage of insuring accuratepositioning of the carrier and voice coil in the magnetic gap regardlessof slight inaccuracy, in securing the carrier tube to the diaphragm.This effects improvement in the apparatus and saving in assembly cost,since, when the centering device is secured to the diaphragm, the voicecoil carrying tube must be positioned on and secured to the diaphragmwith great accuracy in order that it shall be properly centered withrelation to the magnetic gap.

Other features and advantages of the invention will appear from thefollowing description of an approved embodiment of the invention. In theaccompanying drawing:-

Fig. 1 shows diagrammatically a dynamic speaker embodying the invention;

Fig. 2 is a side view of the voice coil carrier with a coil thereon;

Fig. 3 is an end view of the carrier; and I Fig. 4 is an enlargedsectional view of the voice coil carrier with a coil thereon.

Referring to the drawing, and first to Fig. 1, the dynamic speakerillustrated includes the usual magnetic circuit shown as formed by amagnet of usual form having a central core l0 not extend at all beyondthe inner edge of the coil. The tube should, however, extend outwardsuificiently to have the diaphragm spaced conveniently away from themagnet. The bands 3| and 32 are most desirably of a thicknesssubstantially equal to the thickness of the coil, which is comparativelythin. The inner tubular member 30 is made of strong paper or light paperboard as thin as possible consistent with the necessary strength. Notmuch strength is required in this member, especially with a layer-woundcoil of very thin metallic ribbon as shown.

Such a, voice coil is more particularly described and claimed inapplication of Clifford E. Stevens and William T. Taber, Serial No.366,254, filed May 27, 1929. Most desirably, the successive, insulatedturns of the thin conducting strip or ribbon are cemented together andthe coil as a whole cemented to the inner tubular member 30 of thecarrier. The ends of the coil-forming ribbon are turned outward andsecured to the carrier tube at spaced points as byeyelets 34 and mayextend thence to form the flexible connections 35 to the leads 22.Obviously, coils of other suitable kinds may be used on my carriers, butlayer-wound coil of thin metallic ribbon, aside from its electricaladvantages, has the advantage of contributing to the strength of thecoil device.

The centering member or disk 25 may be of any suitable form and materialgiving the necessary flexibility to permit the desired freedom of axialmovement of the tube while preventing transverse movement thereof. Itneed not be a sheet or plate but may be of any suitable construction toresist movement of the tube in at least three directions in a transverseplane. Most desirably, it is made from a piece of strong butsulflciently flexible material, such as paper or fibre board or verythin metal or Bakelized fabric partly cut away between peripheral andcentral portions to make it more flexible, as, for example, as shown inFig. 3. The central portion of the disk has an opening 31 to receive afastening screw, and the peripheral portion serves as an interiorstrengthening flange for the tube. The disk should be fixed securely,and, most desirably, permanently in the tube. I have found it best tocup or otherwise shape a piece of the sheet material so that it shallhave a flange 36 extending at right angles from the disk proper of asize to fit within the tube, and most desirably of a width to extend tothe edge of the tube when the disk is positioned within the tube. Theflange is cemented or otherwise suitably secured to the tube wall.

What is claimed is:

1. An electro-acoustic device, comprising a magnetic circuit having acentral pole piece and an annular air gap about the end of the polepiece, an acoustic diaphragm, a tubular voice coil carrier attached tothe diaphragm and extending therefrom into the magnetic gap, a flexibledisk serving as a centering member extended transversely within thetubular carrier intermediate its ends and provided with a peripheralflange for attachment thereto, means for securing said disk to the endof the central pole piece, and a voice coil wound around said tubularcarrier.

2. An electro-acoustic device, comprising a magnetic circuit having acentral pole piece and an annular air gap about the end of the polepiece, a dished direct-acting diaphragm, a voice coil, and a tubularvoice coil carrier attached to the apex of the diaphragm and extendingtherefrom into the magnetic gap, a. flexible disk serving as a centeringmember extended transversely within the tubular carrier intermediate itsends and provided with a peripheral flange for attachment thereto, meansfor securing said disk to the end of the central pole piece, and a voicecoil Wound around said tubular carrier.

3. An electro-acoustic device, comprising a magnetic circuit having acentral pole piece and an annular air gap about the end of the polepiece, a dished direct-acting diaphragm, a voice coil, and a tubularvoice coil carrier secured to the small end of the diaphragm andextending therefrom into the air gap, the carrier tube having acircumferential groove in which the coil is located, a flexible diskserving as a centering member extended transversely within the tubularcarrier intermediate its ends and provided with a peripheral flange forattachment thereto, means for securing said disk to the end of thecentral pole piece, and a voice coil wound around said tubular carrier.

4. The combination with a direct-acting conical diaphragm for anelectro-acoustic device, of a tubular voice coil carrier secured to thesmall end of the diaphragm, a flexible disk serving as a centeringmember extending transversely within the tubular carrier intermediateits ends and provided with a peripheral flange for attachment thereto,and a voice coil wound around said tubular carrier.

5. A voice coil carrier for an electro-acoustic device, consisting of ahollow cylinder of non-conducting and non-magnetic material having anexternal circumferential groove for receiving the coil, a flexible diskserving as a centering member extending transversely within the tubularcarrier intermediate its ends and provided with a periph eral flange forattachment thereto, and a voice coil wound around said tubular carrier.

6. A tubular voice coil carrier, having a flexible centering diskextending across the interior thereof and spaced from either endthereof, said disk provided with a flange which constitutes theattaching means to the coil carrier.

'7. A tubular voice coil carrier, having an external circumferentialvoice coil groove, and having a flexible centering disk extending acrossthe interior thereof spaced from either end thereof and close to atransverse plane extending through the groove, said disk provided with aflange which constitutes the attaching means to the coil carrier.

8. A voice coil device for an electro-acoustic device, comprising ahollow cylinder of non-conducting and non-magnetic material, and a voicecoil mounted in an externally reduced portion of the cylinder and havingits outer surface substantially flush with the outer surface of thecylinder, the cylinder having a flexible disk extending across theinterior thereof to serve as a centering member, said disk provided witha flange which constitutes the attaching means to the coil carrier.

9. In telephonic apparatus of the character described, the combinationwith a conical diaphragm of large diameter, of a field pole plate and apole spaced therefrom to form an air gap, a voice coil disposed foraxial vibration in said air gap, a form for said coil having anelongated neck projecting beyond said pole plate, means for securingsaid diaphragm to the end of said neck remote from said coil, and a leadfrom said coil anchored to said neck between said coil and the adjacentend of said diaphragm, said lead extending flexibly from said anchorageto the external circuit. said anchorage disposed at such point on saidneck that at maximum axial vibration of said coil the flexible portionof said lead is prevented from contacting with said pole plate.

10. A movable member for an acoustical device comprising a diaphragm, anannular support of insulating material connected to said diaphragm, acoil of wire wound on said annular support, a lead-out for each end ofthe wire of the coil comprising a flexible conductor connected thereto,and means for attaching each flexible conductor at its connected end tosaid support alone.

11. The method of manufacturing a driving coil for attachment to adiaphragm of an acoustical device which comprises forming an annularsupport from insulating material, winding a coil of wire on saidsupport, electrically connecting to each end of the wire of said coil aconductor of flexible material, and fastening one end of each conductorto the support at a point adjacent its connection to said wire, saidfastening being independent of said diaphragm.

12. In telephonic apparatus, the combination with a diaphragm, of avoice coil for actuating said diaphragm, an annular form on which saidvoice coil is disposed and which extends at substantially the diameterof said coil to said diaphragm, a lead for connecting said voice coil toan external circuit taking off directly from said coil form andindependently of said diaphragm, and means defining the point of takeoff comprising means for anchoring the lead to the coil form at a pointbetween said coil and said diaphragm.

WILLIAM T. TABER.

